Wireless Data and Power Transmission Aiming Intracranial Epilepsy Monitoring
This study presents a wireless power and data transmission system to overcome the problems in intracranial epilepsy monitoring associated with transcutaneous wires. Firstly, a wireless power transfer link based on inductive coupling is implemented and a power management unit for the implant is designed. 4-coil resonant inductive link scheme is exploited since it exhibits a high efficiency and optimal load flexibility. Power management unit consists of an active rectifier, a low drop-out voltage regulator which is biased internally with a supply independent current source; all implemented as integrated circuit. Wireless power link provides 10 mW under 1.8 V dc to the load, more specifically the electrodes and read-out electronics. Wireless data communication is realized using the same frequency, 8.4 MHz, as the power link. Load shift keying is performed for uplink (from implant to external) communication by switching an integrated modulator which, in fact, detunes the resonance. Modulated signal is recovered on the external device by means of an integrated self-referenced ASK demodulator. Data rate is adapted for a fast ripple (< 500 Hz) detection system which requires 300 kbps communication. The measurements show that the system works at 36% power transfer efficiency without communication link and the efficiency drops to 33% with 300 kbps uplink data transfer. Finally, in-vitro tests that emulate the real operation scenario are performed thanks to the two-polymer packaging and almost the same power transfer efficiency is achieved under same operation conditions.